Principles of Synchronous Digital Hierarchy

347Operations and Maintenance in SDH

of parameters for various activities such as alarm, order wire, traps routing,

disconnections and reactivations of the links, automatic protection switch-

ing, programming, billing, etc., are some of the other activities that the man-

agement needs to carry out on a regular basis.

All these functions are carried out with the help of a network management

system (NMS).

The NMS in SDH is provided through the use of DCC bytes. There are

three bytes in the regenerator sections D1 to D3, facilitating a data commu-

nication channel of bit rate 3 × 64 kbps = 192 kbps. This is called the DCC

R

channel. Similarly, there are nine data communication bytes, i.e., D4 to D12

in the multiplex section, facilitating a data commun ...